Waveguides used in transmission of microwave radiation have either a rectangular or circular cross-section. In various systems it is at times necessary to provide a junction between those two kinds of waveguides.
One type of junction between a circular and a rectangular waveguide is of a kind in which the internal cross-section gradually changes from circular to rectangular. However, such junctions are generally relatively long (typical length of about 25-65 mm for typical millimeter wave frequency bands) and are thus unsuitable for various applications in which components have to be compacted in a small volume. Additionally, such junctions require that the rectangular and the circular waveguides be co-directional.
Another type of junction between a circular and a rectangular waveguide is of a kind in which the rectangular waveguide opens into the circular waveguide in a mid-point thereof in a manner that its broad side is parallel to the longitudinal axis of the circular waveguide. In such a junction only one polarity of a wave will be transmitted from the circular waveguide to the rectangular waveguide and thereby it is useful as a polarity selector. Additionally, an arrangement comprising two such junctions at right angles to one another may be used as a summator or separator of waves of different polarities.
To date, no junctions for coupling a circular waveguide to a rectangular waveguide, which are of a small size and which transmit the energy between the two waveguides at high efficiency, are available.
Waveguides can operate basically in two transmission modes: TE modes in which the electric field has only a transverse component and TM modes in which the magnetic field has only a transverse component. The present invention concerns only waveguides operating in the fundamental and some higher TE transmission modes.
It is the object of the present invention to provide a junction between a circular waveguide and a rectangular waveguide both operating in TE modes which is of a small size and which transmits the energy between the two waveguides at high efficiency.
The most common mode of operation of a rectangular waveguide is the TE.sub.10 mode and the most common mode of operation of a circular waveguide is the TE.sub.11 mode. The explanation of these two modes of operation is beyond the scope of this writing, but is no doubt clear to the artisan.
It is accordingly a particular object of the present invention to provide a junction between a rectangular waveguide operating in the TE.sub.10 mode and a circular waveguide operating in the TE.sub.11 mode.
It is a further object of the present invention to provide a coupling device between a circular and a rectangular waveguide comprising the above junction.